(1) Field of the Invention
The present invention relates to a photosensitive material for electrophotography having an organic photosensitive layer formed on an aluminum substrate of which the surface has been treated, and more particularly to an organic photosensitive material having improved developing sensitivity.
(2) Description of the Related Art
Photosensitive materials for electrophotography which are widely used are obtained by forming various inorganic or organic photoconductive layers on an electrically conductive substrate. Among such organic photosensitive materials, there has been known a so-called function-separation type photosensitive material based on the combination of a charge-generating substance and a charge-transporting substance in a laminated form or in a dispersed form.
Commercially, a drum of aluminum has in many cases been used as an electrically conductive substrate for forming an organic photosensitive material. To accomplish intimate adhesiveness with respect to the organic photosensitive layer, the surface of the drum made of aluminum is usually subjected to the anodic oxidation treatment or so-called Alumite treatment.
In the electrophotographic system of either the analog type or the digital type, in general, it is desired to employ a developing system having a high developing sensitivity, i.e., having a large .gamma. (gamma) value in order to reproduce high-contrast images such as characters. Here, the .gamma. value is defined as an inclination when a relationship is plotted between the image concentration which is represented by an ordinate and an electrostatic latent image potential (or a bias potential) represented by an abscissa.
In the conventional electrophotographic method, the .gamma. value varies depending upon the constitution and characteristics of the photosensitive layer, as a matter of course. When the photosensitive layer is constant, it has been known that the .gamma. value varies depending upon the characteristics of the developing agent or the conditions of the developing system.